Existing object sizing technologies include dynamic light scattering, laser light diffraction, mechanical sieves, video imaging, image analysis, and scanning light beam projection. The technologies are limited to analyzing groups of objects, without providing detailed information on dimensions or imperfections of individual objects, and have other limitations as well. These technologies are limited to creating two-dimensional object signatures or object cross sections, with no ability to do three-dimensional (3D) sizing analysis. Many times, the measured object is stationary with the beam scanning the object multiple times in order to obtain a size measurement. Some of these measuring techniques, for example, use only a single light sheet or beam. A single light sheet or beam apparatus allows for only a single variable, however, which is insufficient for calculating velocity. Such an apparatus can detect the presence of an object when the light is shadowed, but has no way of calculating the object size without knowing the object velocity. Thus a single light sheet or beam is unable to determine object velocity, requiring that object velocity be known in advance or input into the measurement device. This is problematic, as object velocity often varies or is unknown, such as with freely falling objects.
For analyzing large numbers of objects or a steady feed, video imaging and image analysis technologies are employed, but are speed-limited because of limitations on processing power available to perform the associated computer computations. Another object measurement methodology uses scanning light beam projection. Scanning light beam projection is used on single objects in a process line and requires the object to be moving at a known or predetermined velocity. Scanning light beam projection also typically uses rotating mirrors, potentially leading to inaccuracies.
There are several apparatuses embodying one or more of these techniques. One such apparatus is disclosed in U.S. Pat. No. 4,659,937. This patent is described as a laser beam focused on a single axis using a combination of cylindrical lenses and a laser-detector pair used to detect defects and measure wire diameter. Another reference (U.S. Pat. No. 6,927,409) is described as disclosing the monitoring of the drawing of wire or metal bar stock using rotary optical sensors to determine a product type and to detect product defects. The rotary sensors measure the part in two dimensions using polar coordinates. The sensor output is compared to known product standards to determine the presence and type of product and to detect any defects.
Yet another reference (U.S. Pat. No. 4,917,494) is described as disclosing a time-of-flight optical system that uses two closely spaced and substantially parallel light beams for measuring particle sizes by recording the time-of-flight between the two beams. Each light beam has a thin elongated cross-sectional shape and the particles are passed through the apparatus in a vacuum stream. Another reference (U.S. Pat. No. 5,164,995) is described as disclosing an apparatus for measuring parts on a process line. The parts typically move on a planar track between an optical emitter and a detector pair, with compensations for voltage variations due to any variation in vertical motion.
Other examples are disclosed in three references (U.S. Pat. Nos. 5,383,021; 5,568,263; and 6,285,034), described as disclosing a non-contact multi-sensor bolt-sizing apparatus in which bolts move along a track, partially blocking laser beams to create shadows on corresponding detectors. The disclosed apparatuses are described as using sheets of laser light, both parallel and perpendicular, to produce two-dimensional part images. These apparatuses are unable to detect a part's velocity, however, unless the part size is known in advance or obtained from evaluating part profile information. Additionally, the parts must also be directed in a desired orientation on a track in order to be measured. None of these references disclose a way to measure parts in three dimensions moving at an unknown velocity. They are limited to two-dimensional object signatures or two-dimensional object cross sections.